At least 16 people have reportedly been killed in the US city of Lewiston, Maine and a search is under way for the gunman.
The shootings began at 18:56 local time (22:56 GMT) on Wednesday at a bowling alley and a restaurant, police said.
Lewiston residents, as well as those in the nearby town of Lisbon, have been told to shelter in place.
Police named Robert Card, 40, as a person of interest and said he should be considered “armed and dangerous”.
The authorities have not yet confirmed a death toll but CBS, the BBC’s US partner, has said the number is at least 16 after speaking to multiple law enforcement officials.
There have also been multiple but unconfirmed reports of at least 50 people injured.
Michael Sauschuck, commissioner in Maine’s Department of Public Safety, said there had been “multiple casualties”.
Lewiston has a population of around 38,000 people and is the second-largest city in Maine after Portland.
Lewiston police said officers had responded to reports of shooting at two locations, a restaurant called Schemengees, and Sparetime Recreation, a bowling alley, which appear to be about four miles (6.5km) apart.
Riley Dumont told ABC News her 11-year-old daughter had been taking part in a children’s bowling league at the bowling alley when she heard several gunshots.
She said her father, a retired police officer, had then corralled their family into a corner.
“I was laying on top of my daughter,” she said. “My mother was laying on top of me.”
She added that she saw three or four apparent victims.
Billie Jayne Cooke, who is running for the city council in Lewiston, told BBC News Channel she had been leaving an event as details of the shooting emerged.
“Helicopters, sirens, I’ve never heard so much activity in my life in this city. We have police from all over the state, from out of the state, coming up,” she said.
“The whole city’s on lockdown. It’s horrible. You just don’t think that’s ever going to happen and it did.
In a statement on X, formerly Twitter, Maine State Police said: “There is an active shooter in Lewiston”.
The Androscoggin County Sheriff’s Office released images of a person of interest, saying he was at large and asking for the public’s help identifying him.
They showed a bearded man in a brown sweater carrying a firearm walking into a building.
Robert Card is a firearms instructor who was trained by the US military at a facility in the city of Saco, Maine, according to a state police bulletin seen by CBS.
The bulletin also said he had spent time in a mental health centre in the summer of 2023 and had threatened to commit a shooting at the base.
The authorities also shared a photo of a white vehicle, saying its front bumper was believed to be painted black, and asked anybody who recognised it to contact police.
Mr Sauschuck told reporters that residents in Lisbon had been asked to shelter in place because that was where the vehicle was located.
The Central Maine Medical Center said it was reacting to a “mass casualty, mass shooter event” and was coordinating with other hospitals in the area to treat the injured.
Lewiston Public Schools Superintendent Jake Langlais said in a statement that schools in the district would be closed on Thursday.
A statement from the Department of Homeland Security (DHS) said Secretary Alejandro Mayorkas had been briefed and was continuing to monitor the situation.
A US justice department statement said that federal agencies were assisting state and local law enforcement.
The White House said President Biden had spoken individually by phone to Maine Governor Janet Mills, Senators Angus King and Susan Collins, and Congressman Jared Golden.
Senator King said in a statement he was “deeply sad for the city of Lewiston and all those worried about their family, friends and neighbours”.
